In lithium ion batteries storing high density internal energy, excessive accumulation of internal heat while in the over-charged state could damage battery performance and life, and, in particular, may result in a battery explosion and even fire. Therefore, such lithium ion batteries must have a well-designed protective circuit to ensure safety during the over-charged/discharged states and to prevent performance deterioration as well. Most of the available integrated circuits for protection of lithium ion battery packs (hereinafter IC) utilizes pure analogue circuits. Different reference voltage source ICs produced with CMOS technology using different doping concentrations are not completely the same, and the thresholds for over-charging/discharging protection will vary within a certain range. A large number of divider (bleed) resistors can be designed into the IC by the designer based on such variations. There are also a large number of regulation points (for adjustment of variations) that can be designed in to adjust the resistors. Both of these approaches allow it possible to adjust the divider (bleed) resistance during intermediate testing according to the desired voltage ratio and after the wafer has been manufactured. As a result, the resistance may be kept basically constant to meet the use requirements or specification. Normally, the IC has a number of variable resistors, comparator and reference voltage sources, occupying about 40% of the IC area. The accuracy of such adjustment remains relatively low, and the protective voltage threshold of each battery has to be corrected separately. To ensure adequate accuracy, laser is adopted to adjust to around 100 regulation points for 3˜4 batteries, thus increasing production cost accordingly. Therefore, it is desirable to have a simpler and more cost effective protective circuit for the charging and discharging and inspection of battery packs.